PWM GPIO

This code example demonstrates the configuration of pulse width modulation (PWM) to control the brightness of an LED, and configuration of GPIO to toggle an LED ON and OFF using the Eclipse IDE for ModusToolbox™ software. This application also demonstrates how to invert the PWM signals which would be helpful for applications such as motor speed and direction control.

View this README on GitHub.

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Requirements

• ModusToolbox™ software v2.4.

• Board support package (BSP) minimum required version: 3.0.0

• Programming language: C
• Associated parts:
  • AIROC™ CYW20819 Bluetooth® & Bluetooth® LE system-on-chip
  • AIROC™ CYW20820 Bluetooth® & Bluetooth® LE system-on-chip
  • AIROC™ CYW20719 Bluetooth® & Bluetooth® LE system-on-chip
  • AIROC™ CYW20735 Bluetooth® & Bluetooth® LE system-on-chip
  • AIROC™ CYW20835 Bluetooth® & Bluetooth® LE system-on-chip

Supported toolchains (make variable ‘TOOLCHAIN’)

• GNU Arm® embedded compiler v10.3.1 (GCC_ARM) - Default value of TOOLCHAIN

Supported kits (make variable ‘TARGET’)

• CYW920820M2EVB-01 evaluation kit (CYW920820M2EVB-01) – Default value of TARGET
• CYW920835M2EVB-01 evaluation kit (CYW920835M2EVB-01)
• CYW920719B2Q40EVB-01 evaluation kit (CYW920719B2Q40EVB-01)
• CYW920735Q60EVB-01 evaluation kit (CYW920735Q60EVB-01)
• CYW920819EVB-02 evaluation kit (CYW920819EVB-02)
• CYW920820EVB-02 evaluation kit (CYW920820EVB-02)

Hardware setup

This example uses the board’s default configuration. See the kit user guide to ensure that the board is configured correctly.

Software setup

Install a terminal emulator if you don’t have one. Instructions in this document use Tera Term.

This example requires no additional software or tools.

Using the code example

Create the project and open it using one of the following:

Operation

Using two Bluetooth® SoC boards:

1. Connect the two boards to your PC using the provided USB cable through the USB connector.

2. Open a terminal program and select the WICED PUART COM port. Set the serial port parameters to 8N1 and 115200 baud. You need two windows of the terminal application to view messages from the GATT Server device and the GATT Client device.

3. Program one board with the ‘PWM GPIO’ application.

   Using Eclipse IDE for ModusToolbox™ software

   
   
   1. Select the application project in the Project Explorer.
   
   2. In the Quick Panel, scroll down, and click \ Program (KitProg3_MiniProg4).
   
   Using CLI

   
   
   From the terminal, execute the make program command to build and program the application using the default toolchain to the default target. The default toolchain and target are specified in the application’s Makefile but you can override those values manually:
   make program TARGET=<BSP> TOOLCHAIN=<toolchain>
   
   Example:
   make program TARGET=CYW920819EVB-02 TOOLCHAIN=GCC_ARM
   

4. After programming, the application boots up automatically. Initially the PWM duty cycle is configured as 0, and LED1 is ON. The device trace on the PUART will show basic configurations of the PWM.

   Figure 1. PUART terminal output after booting up

   

5. Press the user button (SW3) to vary the PWM duty cycle between 0% and 100%. When SW3 is pressed initially, the PWM duty cycle on LED2, pin D6, and pin D7 will start changing. This results in the brightness change in a ramping fashion on LED2. In addition, LED1 toggles from ON to OFF.

6. Press the user button SW3 again. LED2 will hold its brightness level at which the button was pressed. LED1 toggles from OFF to ON. The UART terminal shows the duty cycle at which the PWM is stopped. Pin D6 and D7 will also hold the same duty cycle.

   Note: The PWM output on D6 and D7 will be inverted with respect to each other.

   Figure 2. PUART terminal output

   

Debugging

You can debug the example to step through the code. In the IDE, use the PWM_GPIO Debug_JLink configuration in the Quick Panel. For more details, see the “Program and debug” section in the Eclipse IDE for ModusToolbox™ software user guide: {ModusToolbox™ software install directory}/ide_{version}/docs/mt_ide_user_guide.pdf.

Design and implementation

The PWM GPIO application demonstrates how PWMs and GPIOs can be configured in an application using Eclipse IDE for ModusToolbox™ software. It also shows how the PWM signal and GPIO toggling are controlled using an on-board button. When the device is powered ON, it boots up, initializes the PUART, and initializes the Bluetooth® stack. The Bluetooth® stack callback function (bt_cback) does the device configuration; configures the GPIO, registers interrupts, and starts a thread to control the PWM signal.

The application_start() function is the entry point to this application. It initializes the PUART and routes all debug traces to the PUART. By default, the PUART baud rate is configured as 115,200 bps. You can change this by using the wiced_hal_puart_configuration() function. The application_start function also initializes the Bluetooth® stack (wiced_bt_stack_init()). The Bluetooth® stack callback function (bt_cback()) performs the following operations when it detects the BTM_ENABLED_EVT event:

1. Configures GPIOs (pins D6 and D7) and LED2 for PWM output.

2. Configures LED1 and sets its output to ‘0’ by default. (Note: Pins are active LOW.)

3. Configures the on-board button (SW3) and the register for button interrupt.

4. Creates a thread to control the PWM signal.

Whenever SW3 is pressed and released, the application detects a button interrupt and calls the interrupt callback function (button_cb()). The app toggles values of LED1 and the PWM flag. The button is configured to detect the falling edge of the interrupt signal (for example, GPIO_EN_INT_FALLING_EDGE). If the PWM flag is TRUE, the duty cycle of the PWM signal will start changing between 0% to 100% back and forth in the PWM_control thread function. This continuous change in the PWM signal will create a ramping effect on the LED2 brightness. The duty_cycle is incremented or decremented with a step size which is set in the application (DUTY_STEP_SIZE).

When the PWM flag is FALSE, LED2 will hold its brightness level at which the button was pressed; LED1 toggles from OFF to ON.

The PWM output on pins D6 and D7 are set inverted with respect to each other as shown in Figure 3.

Figure 3. Inverted PWM in pins D6 and D7

This inverted PWM is achieved by setting the initial states of pins D6 and D7 as follows, and configuring them for the PWM signal:

wiced_hal_gpio_configure_pin(CYBSP_D6, GPIO_OUTPUT_ENABLE, GPIO_PIN_OUTPUT_HIGH);
wiced_hal_gpio_configure_pin(CYBSP_D7, GPIO_OUTPUT_ENABLE, GPIO_PIN_OUTPUT_LOW);

The initial states (immediately after programming) of LED1, LED2, and pin D6 and D7 are as follows:

Table 1. Initial states of LEDs and pins

Note: The initial value of pwm_flag is 0.

This application also provides an option to use the auxiliary clock for generating a PWM signal which uses the 24-MHz base frequency. Note that the desired GPIO pin must have already been configured to output for aclk. See wiced_hal_aclk.h for more details.

To enable the auxiliary clock, set ENABLE_PMU_CLK to TRUE in pwm_gpio.c.

#if ENABLE_PMU_CLK
    clk=PMU_CLK;
    wiced_hal_aclk_enable(PWM_INP_CLK_IN_HZ, WICED_ACLK1, WICED_ACLK_FREQ_24_MHZ);
#endif

Note: By default, ENABLE_PMU_CLK is set to FALSE and the app uses LHL_CLK.

Resources and settings

This section explains the ModusToolbox™ software resources and their configuration as used in this code example. Note that all the configuration explained in this section has already been done in the code example. Eclipse IDE for ModusToolbox™ software stores the configuration settings of the application in the design.modus file. This file is used by the graphical configurators, which generate the configuration firmware. This firmware is stored in the application’s GeneratedSource folder.

• Device configurator: Used for enabling/configuring the peripherals and pins used in the application. See the
  Device configurator guide.

• Bluetooth® configurator: Used for generating/modifying the Bluetooth® LE GATT database. See the
  Bluetooth® configurator guide.

Related resources

Other resources

Cypress provides a wealth of data at www.cypress.com to help you select the right device, and quickly and effectively integrate it into your design.

Document history

Document title: CE228938 - PWM GPIO

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